As for the industrial production of chips for the semiconductor industry, integrated circuits on disc-shaped objects are produced by several consecutive process steps. In line with this production it is necessary that the individual disc-shaped carrier, which are in the following also referred to as wafers, need to be transported from one process station to another process station or an inspection station. Usually a so called movable carrier is used hereunto which extracts the wafer from a pile and transports it to a device for the inspection of the wafer, for example. Such a wafer processing apparatus for wafers with a related movable carrier is known from US 2003/0031537 A1, for example. The wafer processing apparatus described therein is also provided with a movable carrier with which the wafers are transferred from a load port to an inspection station.
It is necessary to ensure during the transfer into the inspection device that the wafer is inserted in a processing station in a preferably defined manner, particularly centered. Hereunto, a retainer for holding a wafer is known from US 2006/187445 A1, for example, having four contacting elements onto which the wafer is positioned. For further improvement, a method for determining geometric parameters of a wafer was already suggested in DE 10 2007 010 223. For this purpose, the wafer is inserted by a movable carrier in a retainer, wherein said retainer is equipped with at least three mechanical contacting elements onto which the wafer is positioned. One of the contacting elements is movable. The contacting elements are arranged on the retainer in such a way that they define a geometric figure which is designed in such a way that the center point of the wafer lies within the geometric figure. The position of each contacting element is determined. Each desired geometric parameter of the wafer is then calculated from the position of the contacting elements.